Examine source code of Undo Close Tab V2

{
  "manifest_version": 2,
  "name": "Undo Close Tab V2",
  "version": "1.3",
  "description": "Quickly reopen recently closed tabs from your browser.",
  "permissions": [
    "sessions",
    "tabs"
  ],
  "browser_action": {
    "default_title": "Undo Close Tab",
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "commands": {
    "undo-last-tab": {
      "suggested_key": {
        "default": "Ctrl+Shift+Z",
        "mac": "Command+Shift+Z"
      },
      "description": "Undo last closed tab"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{17c7b253-bd6f-40ad-a752-0f965e2f3328}"
    }
  }
}